1. Field of the Invention
This invention relates to the treatment of aqueous systems and more particularly to biocidal materials that are synergistic against microorganisms typically found in industrial aqueous systems such as cooling water systems, air washer systems and pulp and paper mill systems.
2. Description of the Prior Art
The formation of slime by microorganisms is a problem that is encountered in many industrial aqueous systems. In industrial cooling water systems, for example, the water used is generally city water, and is sometimes untreated river water for large systems. As such, the water is not sterile, with the result that bacteria accumulate in the system. In addition, a significant portion of bacteria is entrained in the air as the system water cascades down the tower fill. This commonly gives rise to a slimy deposit on the surfaces of the system which come into direct contact with the cooling water. Both once-through and recirculating cooling systems employ large quantities of water as a cooling medium, in which formation of slime by microorganisms is an extensive and constant problem.
The slime formation not only aids in the deterioration of the tower structure in the case of wooden towers, but also may tend to clog up the equipment and make it less efficient if allowed to accumulate. Slime carried through the cooling system plugs and fouls lines, valves, strainers, etc. Bacteria carried through the system in the water deposits on surfaces such as heat exchanger surfaces to form slime masses which impede heat transfer and greatly reduce the efficiency of the cooling system. The slime deposits also provide an environment conducive to the growth of anaerobic bacteria which thrive in the low oxygen environment beneath the slime. These anerobic organisms can cause pitting and corrosion of metal surfaces.
In pulp and paper mill systems, slime formed by microorganisms is commonly encountered and causes fouling, plugging, or corrosion of the system. The slime also becomes entrained in the paper produced to cause breakouts on the paper machines, which results in work stoppages and the loss of production time. The slime is also responsible for unsightly blemishes in the final product, which result in rejects and wasted output.
The previously discussed problems have resulted in the extensive utilization of biocides in cooling water and in pulp and paper mill systems. A variety of materials have been used in such applications including chlorine, chlorinated phenols, organobromines, and various organo-sulfur compounds. All of these compounds are generally useful for this purpose but each is attended by a variety of impediments. For example, chlorination is limited both by its specific toxicity for slime-forming organisms at economic levels and by the tendency of chlorine to react, which results in the expenditure of the chlorine before its full biocidal function is achieved. Other biocides are attended by odor problems and hazards in respect to storage, use or handling which limit their utility. To date, no one compound or type of compound has achieved a clearly established predominance in respect to the applications discussed.
The use of biocides may involve the continuous or frequent addition to the systems being treated and may require addition to multiple points or zones within these systems.